The leading edge of a fan blade is generally the thinnest portion of the fan blade, and the area of the blade most exposed to foreign object impact. The tip section of the blade leading edge, being the least structurally supported area of the blade, is generally most at risk of damage, for example due to foreign object damage (FOD).
Although the inlet of a turbofan engine may be provided with a reduced diameter rounded throat, which may shield the blade tips from FOD, the minimum throat diameter is limited by mass flow constraints, which prevent its restriction beyond a certain choke limit. Such limit may prevent the throat from being sized to adequately protect the blade tips. Accordingly, it is generally necessary to increase the thickness of the blade tips to meet the required foreign object damage requirements. Increasing the thickness of the blade tips typically leads to significant losses in fan efficiency, as the tips are usually critical regions of the blades from an aerodynamic perspective.